This invention relates to a microfluidic valve and method for regulating the flow of minute quantities of liquid.
Microfluidic systems are very important in several applications. For example, U.S. Pat. No. 5,445,008 discloses these systems in biomedical research such as DNA or peptide sequencing. U.S. Pat. No. 4,237,224 discloses such systems used in clinical diagnostics such as blood or plasma analysis. U.S. Pat. No. 5,252,743 discloses such systems used in combinatorial chemical synthesis for drug discovery. U.S. Pat. No. 6,055,002 also discloses such systems for use in ink jet printing technology.
Valves and pumps are the two most fundamental components in controlling the fluid dynamics in a microfluidic system. Various efforts have been made to build miniature valves and pumps for microfluidic systems by micro-machining silicon. Several valves and pumps have been disclosed using mechanical actuators, such as piezoelectric actuators or spring-loaded magnetic actuators. Examples of these are disclosed in U.S. Pat. Nos. 6,068,751; 5,171,132; 5,272,724; UK Patent 2,248,891, and European Patent 568,902. However, there are problems with these mechanically actuated microfluidic devices since they are complex in design, difficult to fabricate and suffer from a lack of mechanical durability and reliability. In addition, these valves are prone to leak because there are problems in producing a good seal. These problems generally result in the high cost, low productivity, and inoperability of these microfluidic devices.
The compatibility in fabrication of the microfluidic devices with the procedure of semiconductor chip manufacturing industry is another important issue in achieving low cost microfluidic systems with mass production. In addition, for those more sophisticated microfluidic systems, a complex micro-valves and pumps system is often necessary to regulate the liquid in the devices. Therefore, an on-chip integrated circuit to control the individual valves and pumps is highly desired. This also requires the microfluidic devices to be compatible with IC fabrication such as the Complementary Metal Oxide System (CMOS) fabrication in the semiconductor industry.
It is an object of this invention to provide to provide a microfluidic valve for controlling the flow of a material through a microfluidic channel and a method for controlling the flow of a material through a microfluidic channel without any mechanical actuation or moving parts.
It is another object of this invention to provide a microfluidic valve using an integrated heater in combined with a specially formulated thermal responsive solution to control the fluid passing through a micro-fluidic channel avoiding any mechanical actuation.
It is another object of this invention to provide a microfluidic valve that can be readily fabricated using standard CMOS fabrication technology in the semiconductor industry.
These and other objects are achieved in accordance with this invention comprising a microfluidic valve for controlling the flow of a material through a microfluidic channel comprising:
a) a microfluidic channel comprising a passageway,
b) a heater in contact with at least a portion of the microfluidic channel, c) a carrier fluid comprising the material and an amount of thermally-responsive material so that the carrier fluid can be thickened by heat from the heater to cause a reduction in flow of the carrier fluid through the microfluidic channel.
Another embodiment of the invention relates to method for controlling the flow of a material through a microfluidic channel comprising heating a carrier fluid in a microfluidic channel, the carrier fluid comprising the material and an amount of thermally-responsive material, the heating causing the carrier fluid to be thickened by heat to cause a reduction in flow of the carrier fluid through the microfluidic channel.
By use of the invention, a low cost microfluidic valve can be obtained. In addition, the invention can be used with an on-chip integrated circuit to control individual valves.